One of essential requirements for lithographic printing plates is to provide copies having no background stains. Background stains increase particularly in proportion to the storage period after preparation of the printing plate. Printing plates which have no background stains immediately after their preparation undergo formation of background stains over time. This tendency is conspicuous particularly when printing plates are stored at high temperatures and under high humidity. Therefore, presensitized lithographic plates which resist formation of background stains when stored for a long time particularly at high temperatures and under high humidity have been desired.
Many attempts to obtain such lithographic plates have been conducted. For example, there have been known a presensitized lithographic plate comprising an anodized aluminum plate having provided thereon in sequence a subbing layer composed of polyvinylphosphonic acid and a diazo compound-containing light-sensitive layer (West German Pat. No. 1,621,478) (corresponding to U.S. Pat. No. 4,153,461), a presensitized lithographic plate comprising an aluminum support having provided thereon in sequence a subbing layer of polyacrylic acid or the like and a diazo resin layer (West German Pat. No. 1,091,433), a presensitized lithographic plate comprising a polyacrylamide-subbed support having provided thereon a light-sensitive layer (U.S. Pat. No. 3,511,661), a technique of adding a high molecular organic acid to a light-sensitive layer of a presensitized lithographic plate containing a diazo compound and an organic high molecular carrier in the light-sensitive layer for the purpose of improving stability with time of the plate and preventing formation of background stains (Japanese Patent Application (OPI) No. 107238/81 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application")), and the like. However, none of these techniques have exerted satisfactory effects, and, hence, more improvements have been desired.
Japanese Patent Application (OPI) No. 5042/82 (corresponding to U.S. Pat. No. 4,401,743) describes a light-sensitive adduct containing a combination of a diazo resin having a plurality of side chain diazonium groups and a sulfonated polymer having a plurality of sulfonato groups (e.g., sulfonated polyurethane or sulfonated polyester). This adduct, however, fails to attain the effect of preventing formation of background stains and, in addition, performance of a presensitized plate using it is governed by the properties of the sulfonated polyurethane or sulfonated polyester because the adduct is used as a light-sensitive layer itself and, as a result, the applicable scope of the lithographic plate is extremely limited.
Further, Research Disclosure, No. 17712 (January 1979) discloses a light-sensitive lithographic printing plate comprising a grained and anodized aluminum sheet having thereon a subbing layer of a high molecular compound containing sulfonic acid group-containing monomer units as recurring units. This subbing layer is intended to maintain hydrophilicity of non-image area throughout development and press runs and is not provided for improving shelf-life of lithographic printing plates. In fact, in specific examples, a light-sensitive layer comprising poly-1,4-cyclohexylenebis-(oxyethylene)-p-phenylenediacrylate-co-3,3'-[(so dio-iminodisulfonyl)dibenzoate], a dye, a sensitizer and azide for print-out is used, and a plate sample having the light-sensitive layer and having been incubated at 120.degree. F. and 50% RH for 2 weeks cannot be developed with a developer to be used for developing fresh plates and is, therefore, developed with dichloroethane having stronger solvent action.